Species Nomenclature: Naming
the Wild Irises

What's a Species?

When I was young, I learned that the
definition of a species was that two organisms belong to the same
species if they can mate and produce fertile offspring. This
definition was reiterated, perhaps with an occasional refinement or
cautionary exception, in my junior high and high school biology
classes. It is probably the most likely definition for a
nonspecialist to bring to mind.

Alas, things are not so simple, especially if
one is speaking of plants rather than animals. If this definition
were applied at face value to the bearded and aril irises, there
would be only four species: the tetraploids (all of which can breed
with each other and produce fertile offspring) and three diploid
species: attica/pseudopumila, all other diploid bearded
irises, and all the diploid arils.

There is still no consensus among biologists
about the best definition of a species, and in fact some have stated
that no definition can be devised to meet all purposes for which the
term is needed. Suffice it to say that a central notion behind the
concept of species is that each species is a breeding population that
has taken an evolutionary course of its own, separate from related
populations, and consequently developed a set of distinguishing
features.

Although in many instances the differences
between species are obvious, there are many situations where
distinguishing species is problematic, and subjective assessments
come into play. Nature is not obliged to conform to human categories;
evolution is a process involving many gradations and complications.
As populations evolve, the features of the plants differ and change,
but the exact point where the accumulated differences amount to the
existence of a new species is quite arbitrary.

A further complication in the naming of
species is that the knowledge of botanists is never absolutely
complete. Ideally, perhaps, every botanist naming a new species would
know all the details of its distribution, ecology, range of forms,
genotype, and development through time - and have similar knowledge
for all the related species. In reality, a new species may be
described on the basis of a few specimens; the species' connection
with others may emerge only later, after more observations are
made.

Some botanists ("splitters") see significant
distinctions everywhere, and divide populations into many species.
Others ("lumpers") emphasize the similarities instead, subsuming many
different populations under a single broadly defined species. If two
botanists independently name the same species, or name two types that
are later merged into a single species, the result is synonyms: two
or more names that refer to the same species. There are many
instances of this in iris nomenclature.

Within a Species...

Because species are populations of plants,
not individual plants, they can show a great deal of variation. It
can be a surprise, if one is used to growing only named cultivars, to
discover that the same species obtained from two different sources
may differ in height, bloom color, branching, flower size, or any
number of characters. Keeping track of these differences is important
to the gardener or hybridizer. Botanical nomenclature is helpful,
although it does not address every need.

In botany, there are three ranks of
classification below that of species.

The highest is that of subspecies,
abbreviated ssp. In principle, subspecies are populations of a
species that have become reproductively isolated from each other and
are evolving in different directions. Usually, the isolation is the
result of a geographical barrier: a body of water, a mountain range,
or other terrain where the species cannot grow. The implication is
that if the barrier were removed, the subspecies would interbreed
again and merge back together.

The next level is that of variety
(Latin varietas, abbreviated var.). This should not be
confused with the use of the word "variety" in horticulture, which
refers to a named cultivar. A botanical variety is a population that
has some distinguishing qualities, but is not so isolated as a
subspecies. An example might be a population growing at higher
elevations with consistently smaller leaves, lighter colored flowers,
and more compact growth. There may be continuous variation between
the high-altitude variety and its lowland-growing
neighbors.

The lowest level is the form (Latin
forma, abbreviated f.). A form is any plant or group of plants
showing a difference in some character or other, for example, an
albino form with white flowers. There is no implication that each
form is a breeding population or community - these are just plants
that are noticeably different in some way. Botanists, whose interest
is usually in the evolution of populations, usually take less
interest in forms than do gardeners and breeders, for whom these
differences can be intriguing and exciting.

In reality, the distinctions between these
three ranks are not maintained very consistently. Again, the problems
are lack of complete knowledge about a species' range of variation,
and the subjective inclinations of the botanists making use of the
terms. It is not unusual to find the same term regarded as a species
by one author, a subspecies by another, and a meaningless synonym by
a third.

What is the species enthusiast to do, when
the names of the plants are so murky and shifting? This is a very
different world than that of registered cultivars, where many of us
begin our interest in irises. We have been indebted to scholars who,
over the years, have tried to sort this all out and present a
consistent set of names: Dykes, Lawrence, Rodionenko, Mathew,
and others. Most species enthusiasts settle on the most recent such
presentation and use it as an authority for proper naming.

Collectors and plant sellers do not all use
the latest system of choice, however, and many plants are passed down
with names now considered obsolete or incorrect. As a hybridizer,
names are useful for me to the extent that they convey the plant's
distinctive qualities and expected breeding behavior. Thus, although
I. attica is sometimes identified as I. pumila ssp.
attica, the former designation is much better suited to my
purposes. I. attica is a diploid and can not be used
interchangeably with I. pumila in a breeding program. It would
also be inconsistent to grow one plant labeled I. attica and a
virtually identical one labeled I. pumila ssp. attica,
just because I obtained them from people with different
nomenclatural preferences. So although one is tempted to retain the
names of plants exactly as given in the catalog or listing from which
they were obtained, this can create its own kind of
confusion.

My own approach, reflected on this web site,
is to follow a chosen authority (mine is Mathew) on which species
names are valid, and use care to assign each plant to one of these
species. In some cases where Mathew is tentative, I have made my own
judgments based on my needs as a hybridizer (by separating the
diploid I. furcata from the tetraploid I. aphylla, for
example). I retain original names from the source of the plants or
seeds following the species name, without committing to any
particular taxonomic rank. Thus plants purchased as "I. taurica
(blue form)", I identify as I. pumila taurica blue. This
seems a fair compromise between the need for a consistent set of
species names and the need to preserve original identifications
attached to the plants or seeds.

This way of writing names lacks the precision
of specifically identified botanical taxa (e.g., I. pumila
ssp. taurica), but it seems to me that such precision is
rather illusory in the horticultural world; there are just too many
opportunities for inconsistent terminology and inadequate
identification to creep in. Identifying plants in my garden as
belonging to a particular botanical subspecies, variety, or form
implies a level of scientific rigor that I don't feel is justified by
my own level of expertise in such matters. The most important thing
is to ensure that the species is correctly identified, and that
different plants are noted in my records in a consistent
way.

Addendum: What's a
cultivar?

"Cultivar" is a term coined from the phrase
"cultivated variety". It is a horticultural term, not a botanical
one. A cultivar is a unique garden plant, either a clone or a
true-breeding seed strain. (The first sense is the one appropriate
for garden irises.) A cultivar can be a selected clone of a species,
e. g., 'Ostry White', which is a collected albino clone of I.
aphylla, or (as is more usually the case), an advanced-generation
hybrid with different species in its background, e. g., 'Alpine
Lake', an MDB derived from both I. pumila and the
germanica, pallida, and variegata ancestors of the tall
bearded irises.

The American Iris Society maintains the
international registry of all iris cultivars, except for bulb types.
This ensures that cultivar names are unique and applied to the
correct plants. In recent decades, there has been a growing
appreciation of the value of registering widely distributed species
clones as named cultivars. If a particular plant is to be circulated
and used in breeding, it is helpful to ensure its integrity by having
a published description including any pertinent data on collection
circumstances, parentage, etc. A registered cultivar name is also
immune to shifts of botanical nomenclature which can confuse the
identification of species clones over time.